Single STM tips have been developed for use in scanning tunneling microscopy that consist of a thin wire, or whisker, ordinarily made of tungsten, which is sharpened at one end to a point. Ideally, the point carries only a single atom at its apex. Tips of this kind are described in H. W. Fink, "Mono-atomic tips for scanning tunneling microscopy," IBJ J. Res. Dev, Vol. 30, no. 5, pp. 460-465 September 1986.
A multiple-tip arrangement has been described in published European patent application A-O 194 323 in connection with a particular scanning tunneling microscope. Cantilever beams are formed by etching a planar silicon chip. The beams have six degrees of freedom to move under the control of electrostatic forces. Attached to each one of the cantilever beams is a tunnel tip which can interact with a defined part of a surface to be investigated.
A second multiple-tip arrangement is described in European patent application Ser. No. A-O 247 219 in connection with a distance-controlled transducer employed in a direct-access storage unit. Tips are individually attached to cantilever beams manufactured by etching from a common silicon body. Each of the cantilever beams, and hence each one of the tips, is individually adjustable by an electrostatic mechanism with respect to the surface of the storage medium of the storage unit.
A generally similar multiple-tip arrangement is shown in European patent application Ser. No. A-O 363 550 with an additional feature of having electronic circuitry for each of the tunnel tips integrated on the chip. The electronic circuitry enables the distance of the tips from the surface of an associated storage medium to be controlled.
European patent application Ser. No. A-O 382 192, which relates to a tunnel-current memory apparatus, discloses another arrangement with multiple tunnel tips. In the tunnel-current memory apparatus, a planar array of tunnel tips as well as a storage element are disposed on cantilevers which are driven by a piezoelectric mechanism.